This invention relates to new cross-linkable diisocyanate polyaddition products which contain uretdione groups statistically distributed in their molecular stucture as well as to a process for the production of these polyaddition products and to their use in the production of cross-linked shaped products.
Numerous processes for the production of diisocyanate polyaddition products which contain uretdione groups are already known and techniques for the conversion of such polyaddition products into shaped cross-linked synthetic resins such as foils, elastomer threads, etc. by allophanate and/or biuret cross-linking have been described, see German patent specifications Nos. 952,940 and 968,566 and German Auslegeschriften Nos. 1,014,740 and 1,153,900.
As described in an earlier application of the present applicant (published Dutch patent application No. 71,12501), isocyanate prepolymers which contain uretdione groups can be converted, according to the existing state of the art, into polyurethanes which contain uretdione groups, by reacting them with diols as chain-lengthening agents in the usual manner. It was not expected that isocyanate prepolymers containing uretdione groups could enter into a similar chain-lengthening reaction with highly reactive chain-lengthening agents such as primary and/or secondary aliphatic polyamines without loss of the uretdione groups since it is stated in this Dutch Patent Application that the unretdione group reacts practically instantaneously with aliphatic amino groups, the reaction resulting in the opening of the unretdione ring.
It has now surprisingly been found, however, that polyisocyanates which contain uretdione groups can be reacted with aliphatic and, in particular, cycloaliphatic diamines or hydrazines without loss of the uretdione ring. This unexpected reaction makes possible the production of numerous novel polyurethane polyureas which could not previously be synthesized, in which urea segments are situated in the immediate vicinity of the uretdione ring. These products are distinguished from the uretdione polyurethanes already known in the art by their improved mechanical strength, reduced tendency to dissolve and reduced tendency to swell on account of their increased degree of physical cross-linking.